Aerofoil



I 28 1925. Juy v. CRONSTEDT ROFOIL Filed Oct. 31, 1921 .Patented anyzs, 1925.

ounce s'ra'rss PATEN orricn.

VALDEMAR CRONSTEDT, OE LANSDOWNE, PENNSYLVANIA, ASSIGNOB TO FEDERAL I ENGINEERING COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

AEBOFOIL.

Application flled October 31, 1921. Serial 1%. 511,751.

Toall whom it may concern; I

Be it known that I, VALDEMAR CRONBTEDT, a subject of the King of Sweden, residing at 27 Highland. Avenue, Lansdowne, in the county of Delaware and State of Pennsyl- Vania, have invented certain new and useful Improvements in Aerofoils, of which the following is a specification, reference being had therein to the accompanying drawing.

This invention relates to an aerofoil for airplanes and the like, and more particularly to a wing structure for an airplane.

The load supporting capacity, or lift, of an aerofoil is partly dependent upon the shapethereof and the object to be attained in aerofoil design is a maximum of lift and a minimum of resistance to forward movement, commonly known as drag. At a given speed the action of the air stream upon the convex concaveaerofoil, as now generally used, is such: as to impart to the same a high lift and also a high drag. On the other hand an aerofoil which is convexoconvex in cross section with its maximum diameter near the lower surface thereof will have a low drag and a correspondingly low lift and will, therefore, require an air flow of higher speed in order to attain and maintain the desired lift. Neither construction is practical for commercial airplane work. I

The purpose of thepresent invention is to provide an aerofoil which will combine within itself the desirable characteristics of both the above mentioned types, thus producing an aerofoil havinira relatively high lift and a relatively low I A further object of the invention is to provide such an aerofoil which will be simfile in its construction and of a strong, dura- 1e character.

In the accompanying drawings Fig. 1 is a front elevation of a monoplane embodying my invention; Figs. 2, 3, t and 5jare dimvrammatical views of a portion of the aerooil and Fig. 2 shows a portion of the aerofoil in perspective; Fig. 3 is a section taken on the line 3-3 of Fig. 2;'Fig. his a section taken on the line Hot Fig. 2;an'd Fig. 5 is a section taken on the line 5-5, of Fig. 2.

In these drawings 1 have illustrated one embodiment of my invention and have shown the same as embodied n the wing structure ot a monoplane, in which the aerofoil is of the internally braced type. It will be understood, however, that the invention maybe employed in airplanes of various kinds and that the aerofoil may be of any suitable construction and material so long as it has the essential characteristics of shape herein set forth.

In carrying out In invention and in order-v to secure the desire characteristics of high as, low drag, and high 11a dragf ratio 1, here shown, one portion thereof Fig. 3,-

has its upper surface Z'curvedupwardly from its front edge to its rear edge and has its lower surface 3 curved downwardly from its front edge to its rearedge, so that this portion of the aerofoil'is convexo-convex in cross section. The maximum diameter of the section, or the line on which the upper and lower surfaces meet, is arranged nearer the bottom surface than to the top so that the oonvexityof the lower surface is less than the convexity of the upper surface of the section. upon a section of this shape is such as to produce a low lift and a very small drag. t will be understood by an ins ection of the The action of the air stream drawings that the curves of t e upper and lower surfaces of the section are not de scribed about fixed axes but are irregular in shape so that the greatest thiclmess of the section is in front of the longitudinal center line of the aerofoil. Another portion of the aerofoil, which is located at some distance from the section of Fig. 3 has its upper surface 2 curved upwardly from its front edge to its rear edge and'conforming substantially to the upper surface of the section of Fig. 3. (Fig. 5.) The lower surface 4 of this portion of the acrofoil is elm curved u wardly from its front edge to its rear e ge, thus imparting to this portion of the aerofoil a convexo-concave shape in cross section. As has been explained, an aerofoil of this shape has a relatively high lift but also a relatively highdrag. The intermediate portions-of the aerofoil, that is, those portions lying between the sections of Fig. 3 and Fig. 5 are of different shapes and, preferabIy, they gradually change from the shape of the section of Fig. 3 to the shapeof the section of Fig. 5, thereby providing the aerofoil with a continuous lower surface, each successive portion of which is of a cross sectional shape different from the.

cross sectional shape of the adjacent portions. In the form here shown that portion of the aerofoil substantially, midwayfl between the sections of Fig. 3 and F ig.,5 has its lower surface extending in substantially a straight line from the leading edge to the trailing edge of the aerofoil. understood, however, that the cross sectional shape of different portions of the aerofoil mag vary greatly from those here shown an that their arrangement relatively one to the othermay also vary. As a matter ofwill operate satisfactorily in an air stream of less speed and is therefore preferably placed away from the propeller slip stream: and this arrangement of the two sections of the aerofoil with the upper and lower surfaces of the aerofoil as a whole converging from the convexo-convex section to the convexo-concave section having a relatively hig lift anda relatively low drag which, as has been stated, is the ultimate purpose to be attained in a structure of this kind. 1 a

While I have shown and described one embodiment of my invention; 1' wish it to be understood that I do not desire to be limited to the details thereof as various modifications may occur to a person skilled in the.

art. Further it will be. understood that while the invention is designed primarily for use in airplane wings, it is not confined to airplanes but may be employed in connec- Letters Patent is:

It will be roduces an aerofoil tion withother structures, such for example as the fins of a submersible boat.

Havin now fully described my invention what I c aim as new and desire to secure b 1. An aerofoil comprising an elongated member having two non-adwcent portions,

one of said portions being convexo-conve'x 1n cross section and the other of said portions being-'convexo-concave in cross sect1on.

2. An aerofoil comprisin member having two non-ad acent portions, one of said portions being convexo-convex in cross section and the other of said ortions being convexo-concave in cross sectlon, and intermediate portions having cross sectional shapes between the extremes represented by the first mentioned portions.

3. An aerofoil comprisin an elongated an elongated member having two non-ad acent portions,

one of said portions being convexo-convex in cross section and the other of said portions being convexo-concave in cross sectlon, and having its upper and lower surfaces converging from said convexo-convex portion toward said convexo-concave portion.

4. An aerofoil having a substantially uni form upper surface, said surface being curved upwardly from its front edge to its rear edge, and having a continuous lower surface, one portion of which is curved downwardly from its front edge toward its rear edge and another portion of which is curved upwardly from its front edge toward its'rear edge.

5. In an airplane, an aerofoil comprising an elongated member having a portion convexo-convex inv cross section arranged adjacent to the propeller and having a portion convexo-concave in cross section arranged at a point remote from the pro eller.

6. In an airplane, an aerofoi comprising an elongated member having a portion convexo-convex in cross section arranged adjacent to the prope convexo-concave in cross section arranged at a point remote from the propeller, the lower surface of said aerofoil changing gradually in shape from the convex portion to the concave portion thereof. v

In testimony whereof, I affix my signature hereto.

VALDEMAR CRONSTEDT.

Her and having a portion 

